The present invention relates to an axial velocity measurement apparatus using a signal wave for detecting an approaching target.
A method of measuring an axial direction velocity component of a target object utilizing the Doppler effect of ultrasonic wave is known (Jpn. J. Appl. Phys. Vol. 34 (1995), pp. 2515-2518, Pt. 1, No. 5B). Also, a method invented by the present inventor, which enables a measurement of a velocity component in the direction orthogonal to a progressing direction of an ultrasonic wave, involves transmitting an ultrasonic wave to receive a reflected signal from a particular direction by a plurality of elements, repeating the transmission/reception operations a plurality of times, Fourier transforming a received signal corresponding to a particular depth in an array direction, and performing a radial Fourier transformation, considering changes in the Fourier transformed result over time as a two-dimensional signal, to measure a velocity vector (1992 IEEE ULTRASONICS SYMPOSIUM 1187-1190).